In recent years, lithium secondary batteries have been widely used as driving power supplies for small electronic devices such as mobile telephones, notebook-size personal computers and the like, and also as power supplies for electric vehicles and for electric power storage.
A lithium secondary battery is mainly constituted of a positive electrode and a negative electrode containing a material capable of absorbing and releasing lithium, and a nonaqueous electrolytic solution containing a lithium salt. A carbonate such as ethylene carbonate (EC), propylene carbonate (PC) or the like is used as the nonaqueous electrolytic solution.
As the negative electrode for the lithium secondary battery, known are metal lithium, and metal compounds (simple metal substances, oxides, alloys with lithium, etc.) and carbon materials capable of absorbing and releasing lithium. In particular, nonaqueous electrolytic solution secondary batteries using carbon materials capable of absorbing and releasing lithium, for example, coke, graphite (artificial graphite, natural graphite) or the like of those carbon materials have been widely put into practical use.
The above-mentioned negative electrode materials store and release lithium and electron at a low potential on the same level as that of lithium metal, and therefore especially at high temperatures, they have a possibility of reduction and decomposition of many solvents, and irrespective of the type of the negative electrode material, the solvent in the electrolytic solution may be partly reduced and decomposed on a negative electrode, therefore bringing about some problems in that the resistance may increase owing to deposition of decomposed products, that the battery may be swollen owing to gas generation through solvent decomposition and that lithium ion movement may be retarded thereby worsening the battery characteristics such as cycle property and the like.
On the other hand, a material capable of storing and releasing lithium such as LiCoO2, LiMn2O4, LiNiO2, LiFePO4 or the like that is used as a positive electrode material stores and releases lithium and electron at a high voltage of 3.5 V or more based on lithium, and therefore has a possibility of oxidation and decomposition of many solvents; and irrespective of the type of the positive electrode material, the solvent in the electrolytic solution may be partly oxidized and decomposed on a positive electrode, therefore bringing about some problems in that the resistance may increase owing to deposition of decomposed products, that the battery may be swollen owing to gas generation through solvent decomposition and that lithium ion movement may be retarded thereby worsening the battery characteristics such as cycle property and the like.
Given that the situation, electronic appliances equipped with lithium secondary batteries therein expands the range of functions and they are in a stream of further increase in the power consumption. With that, the capacity of lithium secondary batteries is being much increased, and the space volume for the nonaqueous electrolytic solution in the battery is decreased by increasing the density of the electrode and by reducing the useless space volume in the battery. Accordingly, the situation is that even decomposition of only a small amount of the nonaqueous electrolytic solution may worsen the battery performance at high temperatures and the battery may swell. Further, the battery service condition is that the capacity is increased by further elevating the charge voltage, in which, therefore, the electrolytic solution is more readily decomposed.
In particular, the gas generation, if any, not only worsens the cycle property and the storage property but also brings about further troubles in that the batteries, as swollen, could not be housed in a limited battery housing space and also problems in that the safety mechanism for current shutdown or the like may be turned on thereby to make the batteries out of service.
Accordingly, an electrolytic solution is longed for, capable of realizing a battery that has a high capacity and is free from degradation of cycle property and storage property and is not swollen even at high temperatures.
Patent Reference 1 discloses a lithium secondary battery using a nonaqueous electrolytic solution to which are added a carbonate additive such as 4-fluoro-1,3-dioxolan-2-one or the like and an organic sulfonic compound such as divinyl sulfone.
Patent Reference 2 discloses a lithium secondary battery provided with a nonaqueous electrolytic solution containing a halogen atom-containing cyclic carbonate such as 4-fluoro-1,3-dioxolan-2-one or the like and a sulfur-containing compound.
Patent Reference 3 discloses a nonaqueous electrolytic solution secondary battery using a nonaqueous electrolytic solution to which is added a sulfone compound such as bis(allylsulfonyl)methane or the like.    [Patent Reference 1] JP-A 2005-108440    [Patent Reference 2] JP-A 2006-294519    [Patent Reference 3] JP-A 2007-173147